1. Field of the Invention
This invention relates to radar systems, and more specifically to search and tracking pulsed Doppler radar systems.
2. Description of the Related Art
A pulsed Doppler radar receiver must detect moving targets in the presence of ground and rain clutter. The radar return signals from moving targets are separated in frequency from the clutter returns. A pulse Doppler radar uses a coherent pulse train, i.e., a train of pulses that are samples of a single unmodulated sine wave, which is a carrier. Due to the pulsing of the carrier, the signal has a broad band line spectrum, where the lines are separated by the pulse repetition frequency (PRF). In the process of down-converting the signals from the radio frequency (RF) to intermediate frequencies (IF) and to baseband, the clutter PRF lines from the image of the passband may fall in the target frequency band and be falsely detected as targets, since the power reflected from clutter may be much greater than power reflected from the target.
It is common practice in the art to provide IF filters with sufficient image rejection to prevent the clutter image PRF lines from being detected as false targets. This causes the filters to be significantly larger, heavier, and more costly than if the filters were only required to reject the target image.